Composite Map Day 8-14

Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Tuesday August 25, 2026 to Monday August 31, 2026

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 17 2026

Synopsis: Dynamical models favor a potentially major and long duration extreme heat event over the southern tier of the contiguous U.S. (CONUS), with the greatest risk focused over the Southern and Central Plains underneath a potent mid-level high pressure center next week. This mid-level high pressure center may slightly shift westward with time, bringing increased risks for extreme heat across the Southern High Plains, Rockies, and Desert Southwest, with the potential for cooler conditions over the southeastern CONUS later in week-2. Meanwhile, given antecedent dryness, the above-normal temperatures and sub-normal rainfall expected for next two weeks support a Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and Middle and Lower Mississippi Valley.

Hazards

• High risk of extreme heat for parts of the Southern and Central Plains, and adjacent areas of the Mississippi Valley, Tue-Wed, Aug 25-26.
• Moderate risk of extreme heat for much of the Central and Southern Plains, Rockies, Desert Southwest, parts of the Middle and Lower Mississippi Valley, and adjacent parts of the Southeast, Tue-Fri, Aug 25-28.
• Slight risk of extreme heat for portions of the Southwest, Great Basin, Rockies, Central and Southern Plains, Middle and Lower Mississippi and Tennessee Valleys, and Southeastern CONUS, Tue-Mon, Aug 25-31.
• Rapid Onset Drought (ROD) risk for portions of the Central and Southern Plains and the Middle and Lower Mississippi Valley.

Detailed Summary

For Thursday August 20 - Monday August 24: WPC Days 3-7 U.S. Hazards

For Tuesday August 25 - Monday August 31: A continuation of amplified subtropical ridging and accompanying extreme heat conditions throughout the southern tier of the U.S. remains the primary hazard threat in the updated outlook. While the ECMWF maintains a more amplified mean solution of this mid-level ridge feature compared to the GEFS and GEFS AI early, there is good model agreement in regards to the location of the ridge center, where tools show elevated chances of 500-hPa heights exceeding 597 dm from the eastern Four Corners to the Lower Mississippi Valley in week-2. A pronounced ridge axis is also featured in the ensembles extending from the ridge center northward into Canada, supportive of above-normal temperatures and possible extreme heat conditions emerging over portions of the Interior West, Plains, and Mississippi Valley next week. Downstream, both the GEFS and ECWMF ensembles also continue to feature more amplified troughing over the eastern CONUS by early next week, where a higher potential for cooler temperatures look to quell extreme heat risks over the Southeast. While much of the anomalous 500-hPa troughing is favored to weaken later in week-2, dynamical models generally maintain mean troughing over the eastern U.S. Paired with another mean trough that is also favored to persist over the eastern Pacific, the predicted mid-level feature begins to resemble more of an Omega block presentation, implying a stable pattern with little respite to the predominant ridging and summertime warmth for much of central North America later in August.

Based on the latest temperature and heat tools, a high risk of extreme heat remains posted in proximity to the amplified ridge center, and is slightly expanded in coverage across the Great Plains and now valid through Aug 26. Within the highlighted high risk area, calibrated heat tools continue to highlight elevated chances for heat index values exceeding the 90th percentile, Probabilistic Extreme Tools (PETs) show at least 40-60% chances for maximum temperatures exceeding the 85th percentile, and the National Blend of Models (NBM) indicate a number of locations with daytime temperatures approaching daily records. In addition, there is good model support for daytime temperatures exceeding 105 deg F, with heat index values above 110 deg F in the high risk area. Surrounding the high risk area, a moderate risk of extreme heat remains posted based on lesser, but increased chances in the temperature and heat tools exceeding the upper climatological percentiles. The moderate risk area is likewise expanded to include portions of the Southern and Central High Plains where there is an uptick in heat signals in the PETs and raw tools relative to yesterday. Conversely, coverage has been removed over parts of the Mississippi Valley and Southeast, where cooler temperatures are favored due to the aforementioned troughing early in the period. The moderate risk of extreme heat is also extended through day 11 (Aug 28) based on the ECMWF and GEFS ensembles favoring a slight westward shift of the mean ridge center (595 and 594 dm heights, respectively) towards the middle of week-2. A broad slight risk area of extreme heat is also posted for all of week-2, with much of its coverage reshaped to include (exclude) portions of the High Plains and Interior West (southeastern CONUS). Portions of the Northern Intermountain and Northern Plains were considered for inclusion in the slight risk area based on stronger support in the GEFS based heat tools, however due to decreasing sun angles over the higher latitudes of the CONUS during late August, there is less confidence for temperatures reaching hazardous thresholds.

No precipitation related hazards are issued in the updated outlook. Areas that are expected to receive increased precipitation reside along and ahead of the mean trough axes favored over the portions of the western and eastern CONUS. While there is some support for a heavy precipitation risk early in week-2 over parts of the Mid-Atlantic and Southeast in the GEFS, the ECMWF, Canadian and GEFS AI favor drier conditions, precluding any heavy precipitation hazards at this time. The region will continue to be monitored for heavy precipitation risks in upcoming outlooks associated with any stalled frontal activity favored. Across the Desert Southwest, tools are rather muted in regards to any influx of monsoonal moisture to support a heavy precipitation risk. It is worth noting that tools favor an uptick in tropical cyclone activity over the eastern Pacific during the next few weeks, as any transient tropical disturbances could trigger a Gulf of California surge event, and bring a heavy precipitation risk during the period. And despite the current lack of support in the tools, isolated areas of heavy rain remain possible, and this region is prone to flash flooding even with relatively low rainfall totals along dry creek beds (arroyos) and in canyons. Caution should always be exercised in such areas if thunderstorm activity is initiated nearby. Also, some convective activity may result in little or no rainfall while still being capable of generating lightning, which poses a risk of wildfire initiation.

A Rapid Onset Drought (ROD) risk remains designated across portions of the Central and Southern Plains and Middle and Lower Mississippi Valley. Based on the latest soil moisture conditions, the ROD area is expanded to include parts of southeastern Texas and southern Louisiana to the Gulf coast in the updated outlook. This ROD area continues to register 30-day precipitation deficits greater than 2 inches (near or under half of normal), with little rainfall expected during the next two weeks. Furthermore, much of this ROD area is within the moderate risk of extreme heat. This could potentially increase evapotranspiration rates and accelerate surface moisture depletion.

Forecaster: Nick Novella

$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts